A biochemical characteristic of many tumor cells is an active aerobic glycolysis. Oxidative phosphorylation, which is the dominant energy yielding pathway in many normal tissues, retreats to a position of secondary importance in tumor cells. There are many contributing causes for this shift in the pattern of energy metabolism, some being well documented, but many being poorly understood. Previous results obtained in this laboratory with human tumor xenografts in nude mice strongly suggest that adenine nucleotide fluxes of tumor mitochondria are different from those of normal mitochondria. In tumor mitochondria, ATP transport is not stimulated by uncouplers, and transport rates for both ATP and ADP are low. In addition, there is extensive efflux of intramitochondrial adenine nucleotides from some tumor mitochondria, and the efflux is further increased by H+ ionophore uncouplers. One of the specific aims is to characterize both the translocation and efflux of adenine nucleotides with respect to their kinetic parameters, selectivity toward substrates and sensitivity to inhibitors and effectors, such as Ca2+. In the mitochondria of one of the human tumors examined, an astrocytoma, the ATPase activity was low. Experiments are planned to determine if this is due to the presence of excess ATPase inhibitor or to altered interaction of the F1 subunits with each other, and with the mitochondrial membranes. Of equal importance to the energy metabolism of tumor cells are ATP utilizing-systems, such as ATP-driven transport systems. Plasma membranes from many tumors generally contain large amounts of Mg2+-ATPase activity, usually in excess of the Na+, K+-ATPase. Preliminary experiments showed that a minimum of two enzymes are responsible for ATP hydrolysis, these being a Mg2+-ATPase and an ATP diphosphohydrolase. These enzymes will be purified, and antibodies will be prepared. It is hoped that the orientation of these enzymes in the plasma membranes, their physiological functions and their possible roles in transport processes can be evaluated with a better understanding of their catalytic properties and with the aid of the antibodies.